Istanbul has been Constantinople, and Byzantium long before becoming Istanbul. There is even a song about it:
So, Take me back to Constantinople
No, you can’t go back to Constantinople
Been a long time gone, Oh Constantinople
Why did Constantinople get the works?
That’s nobody’s business but the Turks.
According to Pliny, the Elder, the first name of Byzantium was Lygos, a Thracian settlement. Byzantium was founded by the Greeks from Megara in 667 BC. Greek legend says it I the name of a Greek king who led the Megarean colonists, who founded the city.
Briefly in the third century AD, the city was called Augusta Antonina by the Roman Emperor, Septimius Severus (193-211) in honor of his son, Antoninus. I did not know this.
Before the Roman Emperor, Constantine the Great made the city the eastern capital of the Roman Empire, he rebuilt the city and modeled it after Rome. The city was often referred to as New Rome.
In honor of Constantine, Emperor Theodosius II (408-450) made the official name, Constantinople. And I think that is the coolest name of the three that we often refer to. It is also the formal official name during the Ottoman Empire.
They may have used other Byzantine names periodically, and informally, through the fall of the Ottoman Empire in 1923. The modern Turkish name, Istanbul means “in the city”. It is based on the common Greek usage of referring to Constantinople as “The City, as we do now for San Francisco.
Istanbul was the common name for the city, even before the 1453 conquest, by regular citizens. Names other than Istanbul became obsolete in the Turkish language about the time of the Ottoman Empires demise. Most modern western languages adopted the modern name, Istanbul during the 20th century.
So, take your pick. Istanbul sounds exotic, but Constantinople sounds other worldly. Cool. And it has a great song with its name in it.
Some famous Turks: Eliza Kazan, Mary Magdalene, Pliny the Younger, St. Paul, Suleiman the Magnificent, Mustafa Ataturk, St. Nicholas, Osman I, Zaza Pachulia, Hedo Turkoglu, and Enes Kanter. 
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